The present invention relates to an optical time-division switching system.
Since the introduction of optical fibers various attempts have been made to develop optical telecommunications systems having a high speed and large traffic handling capacity. In particular, optical time division digital transmission systems are the most attractive system for future applications. However, the current switching system handles electrical signals; conversion of electrical to optical energy or vice versa is necessary at every junction between optical transmission systems and electrical switching systems. Another disadvantage resides in the fact that while optical transmission systems are capable of transmitting signals at speeds higher than 100 megabits per second, electrical time-division switching systems are not capable of switching at comparable speeds.
To overcome these disadvantages efforts have been made to develop optical switching systems. An optical switching system, shown and described in Japanese Patent Laid-open Publication No. 53-117311, employs optical waveguides of different lengths as delay lines to which optical signals of different time slots are selectively applied through an optical switch to effect the switching of the signals from one time slot to another. Since the maximum delay time is exclusively determined by the length of the waveguides, the prior art system has not sufficient flexibility to accommodate a varying number of customer stations and facilities from one switching office to another. Furthermore, waveguides of substantial length would be required to handle signals of a long frame length, resulting in a large equipment size. Another disadvantage of this system is that a switching loss tends to occur at the connection between the optical switch and the delay lines.